Migration of Grid Web Services

Transcription

1 Migration of Grid Web Services Simon Gregor Ebner Abstract The web services architecture has been broadly accepted as a means of structuring interactions among distributed software services [1]. Especially in the grid environment such as in the Globus Toolkit 4.0 [2] this technology do play a central role. To overcome several limitations/short-comings of ordinary web services for the Grid domain several standards has envolved, namely the Web Services Resource Framework [3] and Web Services Notification [4]. But still there is currently no well defined way to transfer stateful web services from one service container into an other. This paper presents ways for doing so. First all prerequisites and used patterns are described as well as the possible procedures. In the second part a concrete example is discussed. 2 Table of Contents 3 Introduction There are several reasons for the need of an easy relocation of web services.... movable services are scaleable, can be easyly restarted,.... In an other scenario the relocation is necessary to move a service directly onto the node holding the data due to law, security reasons or to increase perfromance (stored precedures, bag of services). Relocation might be also desirable to increase the overall computing power. Increase of the overall computing is due to the fact that there might be some computer architectures more suitable for some kind of computation.... As today GT4 does not provide a mechnism to relocate services, the application on top of the GT4 has to handle this. When talking about the migration of grid web services first the anatomy of these services have to be discussed (see section 4). Afterwards a process has to be defined how a service is moved from one WS-container into another. The different procedures available are discussed in section 5. After the relocation of a service has occured the client has to realize that the service has moved. Section 6 shows which ways are available to make the client aware of the move. For easyness this paper leave security out of scope. 1

2 4 Grid Web Services Ordinary Web Services as described in [?] are by definition stateless. To associate state to a service the Globus Toolkit uses the capablilities of the Web Services Resource Framework WSRF. In WSRF, state is provided within framework components with which the webservice can interact. Stateful resources as defined in WSRF can be single instance or multiple instance resources. Both types only differ in the way the resource is accessed but not how state is kept. All WSRF resources can keep state volatile, i.e. state is in memory and will be lost at WS-container restart, or persistent, i.e. state will survive WS-container restarts. The way the resource keeps state is affecting the way a resource can be migrated. In general, relocating stateless resources is much easier than relocating stateful resources References A grid introduction/overview from IBM [5] An overview from the MaxPlanckGesellschaft [6] Good entry point to stateful web services [7] A comprehensive list of references related to the Globus Alliance and the Globus Toolkit [8] Modeling Stateful Resources with Web Services [1]. This paper classifies webservices in stateless, conversational and stateful resources. The WS-Resource Framework [9] From Open Grid Services Infrastructure to WS-Resource Framework [10] (Transition/comparison OGSI and WSRF) All OASIS WSRF specifications [11] 5 Relocation Web Service When moving the service state must be preserved prerequisite: state must be seperated from logic dependent how state is kept in the stateful resources transfer and deployment service needed a standard way of web service deployment have to be defined (are there patterns for deploying?) transfer data via an other web service, via gridftp,...? (in general: using existing grid service or using other mechanism) 2

3 steps: save state, copy service/state, deploy new service, register new service, de-register old service, undeploy old service 5.1 References web service deployment [12] grid service relocation example [13] GT4 replication service [14] WSDM Web Services Distributed Management [15] a good introduction to WSDM [16] diploma thesis on dynamically deployable stateful web services container [17] VERY IMPORTANT: migrating stateful web services using apache axis and p2p [18] 6 Service Discovery / Publishing There are several ways to make the client aware of the relocation of a service. GT4 mechanisms (service block of GT4) UDDI WS-Notification publish proxy object in old web service container delegating service requests to the new resource in other container... see agent technology resource discovery in ad/hoc networks? loadbalancer? search for a generic approach, not for an approach only for Globus Toolkit 3

4 6.1 References Publish-Subscribe Notification for Web Services[4] Some articles about service discovery [19] UDDI [20] UDDI 3.0 specification [21] UDDI solutions [22] UDDI solution JUDDI [23]: juddi (pronounced Judy ) is an open source Java implementation of the Universal Description, Discovery, and Integration (UDDI) specification for Web Services. UDDI solution UDDI4J [24] : UDDI4J is a Java class library that provides an API to interact with a UDDI (Universal Description, Discovery and Integration) registry. The UDDI Project is a comprehensive, open industry initiative enabling businesses to (I) discover each other, and (II) define how they interact over the internet and share information in a global registry architecture. UDDI is the building block which will enable businesses to quickly, easily and dynamically find and transact with one another via their preferred applications. Web Service Inspection Language WSIL [25] WS-Renewable References (unpublished): Ueber diese noch nicht veroeffentlichte Spezifikation ist derzeit leider nur wenig bekannt. Grundstzlich soll die Handhabung von erneuerbaren Endpoint-References normiert werden, um die Adressierung von WS-Resourcen auf dem neuesten Stand zu halten. 7 Case Study 7.1 Prerequisites Installation/configuration Globus Toolkit [26] Globus toolkit tutorial [2] consists of an excelent examples for stateful resources (singleton/multiple resources) as well as ws lifecycle management and ws notifications. 7.2 Web Service Implementation 7.3 Migration Grid Web Service using a stateless and a stateful single instance resource (relocation and publishing of the new location of the service) 4

5 8 Conclusion References [1] Ian Foster, Jeffrey Frey, Steve Graham, and Steve Tuecke. Modeling Stateful Resources with Web Services. -, [2] globus.org. The Globus Toolkit 4 Programmer s Tutorial. -, [3] Globus Alliance. The WS-Resource Framework. The Globus Alliance, [4] Steve Graham and Peter Niblett. Publish-Subscribe Notification for Web services. -, [5] Daniel Sabbah. Bringing Grid & Web Services Together. -, [6] Max Planck Gesellschaft. Ueberblick Standards und Frameworks der fruehen Grid-Entwicklung. -, [7] Cover Pages. Stateful Web Services. OASIS, [8] Globus Alliance. Research Papers from Globus Alliance Members. The Globus Alliance, [9] Karl Czajkowski, Donald F Ferguson, Ian Foster, Jeffrey Frey, Steve Graham, Igor Sedukhin, David Snelling, Steve Tuecke, and William Vambenepe. The WS-Resource Framework. The Globus Alliance, [10] Karl Czajkowski, Don Ferguson, Ian Foster, Jeff Frey, Steve Graham, Tom Maguire, David Snelling, and Steve Tuecke. From Open Grid Services Infrastructure to WS-Resource Framework: Refactoring & Evolution. -, [11] OASIS WSRF Technical Committee. OASIS Web Services Resource Framework TC. OASIS, home.php?wg abbrev=wsrf, [12] Al Saganich. JSR 109: Web Services Inside of J2EE Apps. O REILLY ON JAVA.com, [13] Gabrielle Allen, David Angulo, Ian Foster, Gerd Lanfermann, Chuang Liu, Thomas Radke, Ed Seidel, and John Shalt. The Cactus Worm: Experiments with Dynamic Resource Discovery and Allocation in a Grid 5

6 Environment. -, -. [14] globus.org. GT4 Replication Services. -, -. [15] OASIS. WSDM Web Services Distributed Management. OASIS, -. [16] Heather Kreger. A little wisdom about WSDM. IBM Developerworks, -. [17] Samuel Mueller. A Dynamically Deployable Stateful Web Services Container with Workflow-Driven Operations. -, [18] Beda Christoph Hammerschmidt and Volker Linnemann. Migrating Stateful Web Services using Apache Axis and P2P. -, -. [19] Hari Balakrishnan, Frans Kaashoek, David Karger, Robert Morris, and Ion Stoica. Looking up data in P2P systems. Stanford University, August Technical Report CSL-TR [20] OASIS. UDDI. OASIS, [21] OASIS. UDDI Version 3 Specification. OASIS, [22] OASIS UDDI Specification Technical Committee. UDDI Solutions. OASIS, [23] apache.org. JUDDI. apache.org, [24] IBM Developerworks. UDDI4J. IBM Developerworks, ibm.com/developerworks/views/opensource/downloads.jsp, [25] Timothy Appnel. An Introduction to WSIL. O REILLY ON JAVA.com, -. [26] globus.org. Globus Toolkit 4 Quickstart. -,